In a co-pending application of Lee R. Zehner, Ser. No. 658,833, filed May 13, 1976, entitled PROCESS FOR THE PREPARATION OF OXALATE ESTERS and incorporated herein by reference, there is disclosed a process for the oxidative carbonylation of an alcohol with oxygen and carbon monoxide in the presence of a specific catalyst system to prepare oxalate esters. While oxalate esters find commercial application as solvents and as dye intermediates and the preparation of pharmaceuticals, there is nothing in the literature describing the vapor phase conversion of oxalate esters to produce the commercially valuable ethylene glycol.
The present invention is directed to an effective method for the vapor phase hydrogenation of oxalate esters to produce ethylene glycol. More particularly, the present process relates to the synthesis of ethylene glycol by hydrogenating oxalate esters at elevated temperatures and at relatively low hydrogen pressures in the presence of a hydrogenation catalyst such as a copper zinc chromite catalyst, a copper/alumina catalyst and other mixed copper and metal oxide hydrogenation catalysts, supported or unsupported, and mixtures thereof and useful as suitable catalysts for the hydrogenation in the vapor phase of an oxalate ester to produce ethylene glycol in high yield.
A number of prior art processes have been proposed for the preparation of alcohols and glycols by hydrogenation of certain esters of monobasic and higher dibasic acids in liquid phase and esters of hydroxy acetic acid in vapor phase reaction systems.
An article by H. Adkins, in R. Adams et al, ed., Organic Reactions, Vol. VIII, Chapter 1, John Wiley and Sons, Inc., New York, 1954, pp. 1-27, sets forth a general mechanism for the liquid phase hydrogenation of esters to alcohols in which it is mentioned that in the liquid phase, diethyl oxalate gives a good yield of ethylene glycol but only with a pressure much higher than normal liquid phase hydrogen pressures, i.e., higher than 4000 psi.
U.S. Pat. No. 2,305,104 discloses a process for the vapor phase hydrogenation of alkyl esters of hydroxy acetic acid utilizing a dual catalyst charged reaction zone at temperatures between 150.degree. C. and 300.degree. C. and pressures from 10 to 1000 atmospheres or higher.
British Pat. Nos. 555,240 and 575,380 disclose processes for the vapor phase catalytic hydrogenation of hydroxy acetic acid and its derivatives (esters) and an ester of glycollic acid respectively at temperatures ranging from 150.degree. C. to 300.degree. C. and pressures of from 10 to 1000 atmospheres to produce ethylene glycol.
Ethylene glycol is a valuable commercial chemical and finds application in deicing fluids, antifreeze, hydraulic fluids, manufacture of alkyd resins, solvents and polyester fibers.